Concentration and distribution of selenium in soils of mainland China, and implications for human health

In China, selenium (Se) deficiency and exceeded Se in soils has resulted in serious endemic Se-related diseases. A nationwide dataset of Se is critically needed for prevention and response of Se-related diseases. The China Geochemical Baselines (CGB) project applied standardized methods to create a geochemical dataset that recorded the concentration of 76 elements, including selenium, in the pedosphere of mainland China. A total of 3382 samples were collected from the A-horizon of soil at depths of 0–25 cm. The concentration of Se was determined by hydride generation atomic fluorescence spectrometry. Strategies for quality control included field duplicates, standard reference materials, and analytical replicates. Measured Se concentrations ranged from 0.010 to 16.240 mg·kg−1 with a median of 0.171 mg·kg−1. The Se concentrations showed large variations across regions. Low-Se soils in China occurred in the Tibet, the southern Xinjiang, and some areas of Inner Mongolia, Shanxi and Qinghai provinces. High-Se soils were found in contiguous areas of Hunan, Guizhou, Guangxi, Guangdong, and Chongqing, and sporadically distributed in Xinjiang, Gansu, Sichuan, Yunnan and other provinces. The distribution is controlled by a combination of the underlying geology, local factors such as the geomorphology and soil type, and human activity. Selenium is essential to human and other animal health in trace amounts but is harmful in excess. Keshan disease (KSD) and Kashin-Beck disease (KBD), which occur in the low-Se geological background, are attributed to Se deficiencies, and endemic selenosis is observed in areas with high-Se soils. This enhanced understanding of Se occurrence could help to improve future Se-related disease management in China.